1. Field of the Invention
The present invention relates to a canister system for use in vehicles or the like, and more particularly to improvements in or to the air intake/exhaust arrangement of a canister system.
2. Prior Art
FIG. 1 schematically shows the air intake/exhaust arrangement of a conventional canister system. Connected to a canister 114 are an air intake passage 121 through which fresh air is drawn into the canister 114 and an air exhaust passage 125 through which air is exhausted from the canister 114 after removal of evaporative fuel components from an evaporative fuel-air mixture by adsorption of the evaporative fuel components by the canister 114. The air intake passage 121 has an air-inlet open end 121a remote from the canister 114, which is formed in a side frame 101 of a body of a vehicle, not shown, and a one-way valve 123 arranged thereacross. The air exhaust passage 125 also has a one-way valve 127 arranged thereacross. The air intake passage 121 and the air exhaust passage 125 are joined together at sides of the respective one-way valves 123 and 127 closer to the canister 114. The air exhaust passage 125 has an air-outlet open end 125a arranged at a lower portion of the vehicle body in opposed relation to a mudguard cover 130 such that the air-outlet open end 125a will not be clogged with mud or the like.
With the above arrangement, evaporative fuel generated in a fuel tank, not shown, at refueling is delivered to the canister 114 to be adsorbed thereby, and air resulting from the removal of evaporative fuel components from the evaporative fuel-air mixture is delivered from the canister 114 into the air exhaust passage 125 and discharged into the atmosphere through its air-outlet open end 125a. On the other hand, when evaporative fuel is purged from the canister 114 to an engine, not shown, fresh air is drawn through the air-inlet open end 121a formed in the side frame 101, into the air intake passage 121 and delivered to the canister 114.
According to the air intake/exhaust arrangement of the conventional canister system, however, a special part such as the mudguard cover 130 has to be employed. Further, although the mudguard cover 130 can prevent clogging of the air-outlet open end 125a of the air exhaust passage 125 with mud or the like, it cannot prevent introduction of water into the open end 125a. If water introduced into the open end 125a is frozen, it causes a decrease in the opening area of the open end 125a, and in the worst case it can clog the open end 125a.
In a canister system where evaporative fuel generated in a fuel tank at refueling is not adsorbed by a canister, when the ambient temperature is so low that water is frozen, the amount of evaporative fuel generated in the fuel tank is very small, causing almost no problem even if the opening area of the air-outlet open end decreases with water freeze-up. In contrast, in the air intake/exhaust arrangement of the conventional canister system as illustrated where evaporative fuel generated in a fuel tank at refueling is delivered to the canister to be adsorbed thereby, if the opening area of the air-outlet open end 125a decreases, the flow resistance of the open end 125a increases such that refueling cannot be carried out in the worst case.